1. Field of Invention
The invention relates to a lubricant control apparatus for an automatic transmission and, more particularly, to a technique for controlling a lubricating oil flow in accordance with the situation of a speed change mechanism.
2. Description of Related Art
In the prior art, the automatic transmission is provided with a hydraulic control unit for feeding a line pressure to control the hydraulic servos of its frictional engagement elements, on the basis of a solenoid signal to be outputted from an electronic control unit, so that the frictional engagement element may be applied/released for a speed change. This hydraulic control unit acts as a feeding means for feeding a secondary pressure for transmitting the power in a torque converter and a lubrication pressure for lubricating the individual portions of the speed change mechanism. Therefore, the hydraulic control unit is usually equipped with a primary regulator valve for regulating the pump discharge pressure to the line pressure, and a secondary regulator valve for regulating the excess pressure to a secondary pressure, so that the excess pressure, as regulated by the secondary regulator valve, is fed as a lubrication pressure to the individual portions of the mechanism.
As one system for controlling the regulating actions of the secondary regulator valve, there is disclosed in Japanese Patent Laid-Open No. 221060/1983 (called herein "Related Art 1") a technique in which a throttle pressure is applied to the secondary regulator valve. According to this technique, the lubricating pressure is regulated according to the throttle opening so that the lubricating oil flow to be fed to the individual mechanism portions accords substantially to the input torque to the transmission, i.e., to the vehicle running load.
There is another technique in which the secondary regulator valve is caused to perform the pressure regulation by applying a governor pressure, as disclosed in Japanese Patent Laid-Open No. 83865/1984 (called herein "Related Art 2"). According to this second technique, the lubricating pressure changes according to the vehicle speed so that the lubricating oil flow accords to the vehicle speed.
Here, the lubricating oil is mostly used to cool the heat generated by the gear meshing portions and the frictional engagement elements of the speed change mechanism. In the Related Art 1, therefore, the load condition is referred to the input torque thereby to feed the lubricating oil in a flow according to the throttle opening. In the Related Art 2, the lubricating oil is fed in a flow according to the vehicle speed by referring the load condition to the rotational speed. More specifically, the aforementioned calorific value is different among the individual portions of the mechanism so that it is not always uniquely determined according to the magnitude of the throttle opening or the vehicle speed.
At a steady run without any shift, the calorific value is dependent upon the power loss, which is different at the individual gear stages established by the speed change mechanism. In this respect, the techniques of the related art do not consider the gear stages but have to set the lubricating oil flow to match the gear stage of high loss so that they may be able to cool by sufficient lubrication for every gear stage. At a time of establishing a gear stage of low loss, therefore, the lubricating oil flow is excessive so that the excessive lubricating oil is agitated by the rotary members of the speed change mechanism to cause a dragging resistance thereby lowering the efficiency of the transmission.
At a shifting time, on the other hand, heat is generated in the frictional engagement elements as these elements are applied and released. In order to remove the heat quickly, therefore, the lubricating oil flow has to be increased at the shift time. In the related art, however, a control cannot be executed to increase the lubricating oil flow especially at the shift time. As a result, the cooling rate of the frictional engagement elements is low. At a busy shift time having frequent speed changes, for example, the temperature of the frictional engagement elements may rise to deteriorate the shifting characteristics. Considering the cooling at this shift time, therefore, the problem of the temperature rise of the frictional engagement elements is solved by increasing the oil flow at the steady run. This setting of the lubricating oil flow further lowers the aforementioned transmission efficiency.